Field of the Invention
The present invention relates to a method for determining and displaying the optimal material thickness when measuring fill levels using radar sensors.
Background of the Invention
The present invention relates to a measuring arrangement with a radar fill gauge, for example according to the delay principle for measuring the fill level in a container according to the preamble of claim 1, several methods for reducing the electromagnetic radiation of a measuring arrangement reflecting from the surfaces of a wall, preferably a synthetic wall, according to the preamble of claims 11 and 14, as well as the use of a measuring arrangement for determining the fill level of a fill good in a container according to claim 15.
A measuring arrangement is described for measuring a fill level in a container using a radar fill gauge, which comprises an adaptation for reducing the electromagnetic radiation reflected by the surfaces of a wall of the container, as well as a method for optimizing the adaptation and for reducing stray radiation, for example radiation reflected by the container walls, with the display devices indicating if interfering radiation has been sufficiently reduced.
Fill level arrangements for determining and/or monitoring a fill level in a container are known in various embodiments. Radar level gauges, for example operating according to the delay principle, emit electromagnetic radiation pulses of a certain wavelength and then detect the temporal progression of the reflected electromagnetic radiation as an echo curve. Here, not only reflections at the surface of the liquid to be measured are detected but also a plurality of stray reflections, such as reflections at the walls of the container, in which the liquid to be detected is stored, reflections at the bottom of the container, or also reflections at the container lid. The sum of reflections generate a signal which is measured as a function of time and which as an echo curve detects usually several maximums and displays them in reference to time. From the progression of this echo curve then the fill level of the liquid located in the container shall be determined.
In FMCW-Radar (Frequency Modulated Continuous Wave) a high-frequency signal is used in which during the measuring process the transmission frequency is altered, for example linearly inclines. Here, the frequency change usually amounts to up to approximately 10 percent of the transmission frequency of the high-frequency signal. The signal is emitted, reflected at the surface of the fill good, and received with a time delay. From the present transmission frequency and the frequency received the difference Δf is formed for further signal processing. It is directly proportional to the distance, i.e. a great frequency difference measured represents a large distance and vice versa. This frequency difference is then converted via a Fourier transformation into a frequency spectrum and then the product distance is calculated. The fill level results from the difference of the fill level and the distance.
Particularly disturbing in radar level gauge arrangements are usually the reflections at the container lid, which, if it is arranged between the level gauge and the fill good, must allow penetration of incident electromagnetic radiation, and thus it must be made from a material that is permeable for incident electromagnetic radiation pulses, for example made from a synthetic material, or it must comprise at least a window through which the electromagnetic radiation pulse emitted by the radar level gauge can penetrate into the interior of the container.
The stray reflections, particularly the stray reflections at the container lid, here lead to the consequence that the fill level of the liquid or the bulk good to be determined and located in the container cannot be determined precisely, which leads to a faulty measurement due to the stray reflections. The stray reflections must therefore be minimized.
The objective of the present invention is therefore to provide a measuring arrangement showing an adaptation by which the electromagnetic waves reflected by the surfaces of the container lid and/or by the surfaces of a wall arranged between the fill good and the radar level gauge are reduced such that the fill level to be determined of the liquid which is located in the container or the bulk good located in the container can be determined more precisely. Another objective of the invention is to provide a method for reducing electromagnetic radiation reflected by the surfaces of the container lid and/or the wall.
The objective is attained in a measuring arrangement and a method, each as described herein.